INTRODUCTION: The aim of this study was to evaluate the effects of remnant root canal medicament, calcium hydroxide on the short and long term sealing ability of mineral trioxide aggregate (MTA) apical barrier. MATERIALS AND METHODS: Fifty single-rooted teeth were prepared and apical resorptions were made using sulfuric acid. The teeth were allocated into two experimental groups and two control groups. In group 1, calcium hydroxide was placed into canals for one week. In group 2, no medication was placed. In both groups, a 4-mm MTA plug was placed in the root canals. The remaining portion of the canal was filled with gutta-percha/sealer. The microleakage was evaluated after 7 days and 3 months using fluid filtration technique. Repeated measurement ANOVA was used for statistical analysis. RESULTS: There was no significant difference in sealing ability between the two groups in either time periods. In both groups, microleakage decreased after three months but this decrease was not statistically significant. CONCLUSION: Medication with calcium hydroxide had no adverse effect on the short and long-term sealing properties of MTA plug.